Structures, systems and methods for joining articles and materials and uses therefor

ABSTRACT

This invention provides novel nanofibers and nanofiber structures which posses adherent properties, as well as the use of such nanofibers and nanofiber comprising structures in the coupling and/or joining together of articles or materials.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.10/825,861, filed Apr. 16, 2004, now abandoned, which is acontinuation-in-part of U.S. application Ser. No. 10/661,381, filed Sep.12, 2003, which claims benefit of U.S. Provisional Application No.60/463,766 filed Apr. 17, 2003, all entitled “STRUCTURES, SYSTEMS ANDMETHODS FOR JOINING ARTICLES AND MATERIALS AND USES THEREFOR.” Theseprior applications are hereby incorporated by reference in theirentirety.

FIELD OF THE INVENTION

The invention relates primarily to the field of nanotechnology. Morespecifically, the invention pertains to nanofibers and nanofiberstructures which posses adherent properties, as well as to the use ofsuch nanofibers and nanofiber comprising structures in the coupling,grasping, holding, and/or joining together of articles or materials.

BACKGROUND OF THE INVENTION

Joining together or holding of articles and/or materials has been commonfor at least thousands of years. Such joining has typically beenachieved through use of adhesives of various types, e.g., exogenoussubstances applied between articles or materials to be joined whichadhere to both of the articles or materials and, thus, join them. Today,modern adhesives are an integral part of life. Typical modern adhesivescomprise what are known as contact adhesives. Such contact adhesives areusually based upon variations of soft sticky polymers of varyingviscosity, which conform to surfaces and adhere through van der Waalsforces, thereby joining surfaces/materials.

While such typical adhesives are quite useful, they do have a number oflimitations. For example, the layer of adhesive necessary to joinsurfaces can be inconveniently thick (e.g., from hundreds of microns tomillimeters, etc.). While that might be acceptable in some situations,it is quite inappropriate in others. Adhesives can also often leavemessy residues. Additionally, adhesives can leak, spread or volatilizefrom their area of application into other nearby areas where they arenot desired. Such spreading can result not only in unintended joining ofmaterials, but can also result in chemical or physical contamination ofsuch other areas.

Furthermore, while a wide range of adhesive compounds exists, themajority of them have a (sometimes limited) range of parametersnecessary for their use. For example, some adhesives do not work above acertain ambient temperature (e.g., the polymers become too fluid and theadhesive either loses much of its adherent property or leaks away).Other adhesives do not work below a certain temperature (e.g., theadhesive becomes brittle and cracks). Additionally, many adhesives aretoxic and/or cause irritation to body tissues which come into contactwith them. Yet other adhesives do not adhere in the presence of water,organic solvents and/or vacuum, etc., while other adhesives require suchconditions.

In addition to exogenous adhesive compounds, other adherents such as“hook and loop” or “touch fasteners'” e.g., Velcro®, have more recentlybeen used to join materials together. However, such systems also areproblematic in typically requiring two groups of specifically shapedfiber groups.

In the context of the above background, research on new adherents andmethods of adhesion has been intrigued by examples of adhesion andadherent ability in the natural world. For example, the ability ofgeckos, spiders and flies to adhere to seemingly shear surfaces has longfascinated researchers. Geckos' ability to stick to surfaces without theuse of an adhesive substance (such as a polymer, etc.) has been underintense scrutiny recently as a model for adhesion.

A welcome addition to the art would be an adherent material or surfaceor a method of adhesion which could be modified to fit differentenvironmental conditions and parameters, which would not migrate tounwanted areas, which would not necessarily require two dedicatedsurfaces, and which would require no external application of resins,carriers, etc. The current invention provides these and other benefitswhich will be apparent upon examination of the following.

SUMMARY OF THE INVENTION

In some aspects the current invention comprises a method of increasingan adherence (or adherent) force between two or more surfaces byproviding a first surface (which has a plurality of nanofibers attachedto it or associated with it), providing at least a second surface, andcontacting the surfaces together (whereby an adherence force between thesurfaces is increased in comparison to any adherence force between suchsurfaces in the absence of the plurality of nanofibers), therebyadhering the surfaces to each other. In some embodiments herein, thesurfaces and the plurality of nanofibers can optionally comprise (and beoptionally independently selected from) such materials as, e.g.,silicon, glass, quartz, plastic, metal, polymers, TiO, ZnO, ZnS, ZnSe,ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, MgS, MgSe, MgTe, CaS, CaSe,CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, GaN, GaP, GaAs, GaSb, InN, InP,InAs, InSb, PbS, PbSe, PbTe, AlS, AlP, AlSb, SiO1, SiO2, siliconcarbide, silicon nitride, polyacrylonitrile (PAN), polyetherketone,polyimide, an aromatic polymer, or an aliphatic polymer. In optionalembodiments herein the nanofibers are non-biological in material or,consist essentially of a non-biological material. In other words, thenanofiber is not, e.g., protein, carbohydrate, lipid, or combinationsthereof. The contacting of the surfaces optionally creates van der Waalsattraction between the surfaces (e.g., typically greater forces thanwould exist between such surfaces in the absence of nanofibers). In someembodiments herein such attraction comprises from at least about 0.1newton per centimeter² to at least about 100 newtons per centimeter², orfrom at least about 0.5 newton per centimeter² to at least about 50newtons per centimeter², or from at least about 1 newton per centimeter²to at least about 25 newtons per centimeter², or from at least about 2newtons per centimeter² to at least about 10 newtons per centimeter².Alternatively and/or additionally, the contact of the surfaces createsfriction forces between the surfaces which, in typical embodiments, aregreater than friction forces that would result from contact of suchsurfaces (or similar surfaces) without the nanofibers. Furthermore, thefirst surface of some such embodiments comprises a surface density ofmembers of the plurality of nanofibers from at least about 0.1 nanofiberper micron 2 to 1000 or more nanofibers per micron²; or from at leastabout 1 nanofiber per micron² to 1000 or more nanofibers per micron²; orfrom at least about 5 nanofibers per micron² to 500 or more nanofibersper micron²; or from at least about 10 nanofibers per micron² to 250 ormore nanofibers per micron²; or from at least about 50 nanofibers permicron² to 100 or more nanofibers per micron². Additionally, in otherembodiments, the first surface and the at least second surface arecomposed of the same material.

Furthermore, in yet other embodiments, the nanofibers are composed ofthe same material as one or more of the first or second substrates.Other embodiments include where the nanofibers are hollow nanotubularstructures. In some embodiments, one or more of the nanofibers comprisesone or more associated moiety. In yet other embodiments substantiallyall nanofibers comprise one or more associated moiety (optionally acoating composed of the one or more associated moiety) which can be afunctional moiety in some embodiments. In some such embodiments suchfunctional moiety can increase van der Waals attraction between thenanofiber and the at least second surface (e.g., so that the attractionbetween the nanofiber and the second surface is greater than the van derWaals attraction between the nanofiber and the at least second surfacein the absence of the moiety) or can increase friction forces betweenthe nanofiber and the at least second surface (e.g., so that when anormal force is applied, the friction between the nanofiber and thesecond surface is greater than the friction between the nanofiber andthe at least second surface in the absence of the moiety). Thefunctional moiety can include or comprise a covalent bond (e.g., createa covalent bond) between the nanofiber and the at least second surface.In yet other embodiments, not only does the first surface optionallycomprise a plurality of nanofibers, but the at least second surface cancomprise a plurality of nanofibers attached thereto also. Also in someembodiments, the nanofibers comprise curled or curved nanofibers (orcompliant nanofibers that can optionally curve or bend) that touch oneor more surface at more than one point and/or which touch one or moresurface by contacting the surface with the side of the nanofiber insteadof, or in addition to, the tip of the nanofiber.

In yet other embodiments, such first surfaces can comprise the surfaceof one or more medical device and such second surfaces can comprise oneor more biological tissue (e.g., tissue, such as a vessel, an organ,bone, flesh, plant material, etc., from an biological organism). Suchbiological tissue can be within an organism (i.e., in vivo or in planta)or can be outside of an organism (i.e., ex vivo, in vitro, or explanta). Furthermore, such biological tissue can comprise an entireorgan (e.g., a whole liver) or can comprise part(s) of an organ (e.g., abiopsy sample or a lobe from a liver). Also, the surface (i.e.,comprising the nanofibers) can optionally touch just a small area of thebiological tissue (e.g., as when a probe or retractor touches aninternal organ) or can touch large percentages or even the entirety ofthe biological tissue (e.g., when a laminar patch comprising adherentnanofibers is placed upon an organ or vessel, etc.). Biological tissuecan optionally come from any living, or previously living, organism(e.g., animal, plant, amphibian, reptile, bird, mammal, primates,nonhuman primates, humans, etc.). Nonlimiting examples of such devicesoptionally comprise, e.g., clamps (e.g., c-clamps, barrel clamps,circular clamps, etc.), stents, shunts, probes, retractors, patchesand/or bandages, laminar sheets, medical meshes, etc. In typicalembodiments, the surface(s) of the device which adhere to the biologicaltissue comprise nanofiber surfaces. Thus, for example, in embodimentscomprising stents, the adherent nanofiber surface is typically thesurface that comes into contact with the biological tissue, e.g., ablood vessel, a meatus, a duct, etc. For example, a stent going inside ablood vessel would typically comprise adherent nanofiber surfaces on theoutside portion of the stent that would come into contact with theinside of the vessel.

In other aspects, the invention comprises a method of joining two ormore articles. Such method comprises providing a first article (with atleast a first surface comprising a plurality of nanofibers attached toit or associated with it), providing at least a second article having atleast a first surface, and mating the first surface of the secondarticle with the plurality of nanofibers on the first surface of thefirst article (so that the nanofibers contact the first surface of thesecond article at a plurality of contact points) whereby forces betweenthe nanofibers and the first surface of the second article adhere thefirst article to the second article (i.e., more than adherence thatmight occur in the absence of the nanofibers). In optional embodimentsherein the nanofibers are non-biological in material or, consistessentially of a non-biological material. In other words, the nanofiberis not, e.g., protein, carbohydrate, lipid, or combinations thereof. Insome typical embodiments such adherent forces comprise van der Waalsforces. In other typical embodiments, such forces can alternatively oradditionally comprise friction forces (e.g., as when a normal force isapplied). Such embodiments optionally comprise a density of contactpoints per unit area (i.e., the contact density or intimate contactarea, etc.) of the second surface. The density of contact points canoptionally comprise contact of from at least about 1 nanofiber permicron² to 2000 or more nanofibers per micron²; or from at least about 5nanofibers per micron² to 1000 or more nanofibers per micron²; or fromat least about 10 nanofibers per micron² to 500 or more nanofibers permicron²; or from at least about 50 nanofibers per micron² to 250 or morenanofibers per micron²; or from at least about 75 nanofibers per micron²to 150 or more nanofibers per micron². Of course, in some embodiments,e.g., when nanofibers curve and touch a surface more than once, themeasurements are typically nanofiber contacts per square micron of thesurface. In some embodiments the plurality of contact points (i.e., thecontact density or intimate contact area, etc.) comprises a percentcontact area of the second surface, which can optionally comprise fromabout 0.1% to at least about 50% or more; or from about 0.5% to at leastabout 40% or more; or from about 1% to at least about 30% or more; orfrom about 2% to at least about 20% or more; or from about 5% to atleast about 10% or more of the area of the second surface. Furthermore,embodiments herein can optionally comprise a plurality of contact pointscomprising a density of contact points per unit area of the secondsurface and comprising a percent contact area of the second surface.Thus, the density of contact points can comprise contact of from atleast about 1 nanofiber per micron² to about 2000 or more nanofibers permicron², from at least about 5 nanofibers per micron² to about 1000 ormore nanofibers per micron², from at least about 10 nanofibers permicron² to about 500 or more nanofibers per micron², from at least about50 nanofibers per micron² to about 250 or more nanofibers per micron²,or from at least about 75 nanofibers per micron² to about 150 or morenanofibers per micron², and can also comprise a percent contact area ofthe second surface from about 0.1% to at least about 50% or more, fromabout 0.5% to at least about 40% or more, from about 1% to at leastabout 30% or more, from about 2% to at least about 20% or more, or fromabout 5% to at least about 10% or more.

In other aspects, the present invention comprises a method of joiningtwo or more articles, by providing a first article having at least afirst surface, providing at least a second article having at least afirst surface; and providing a layer of nanofibers disposed between thefirst surface of the first article and the first surface of the at leastsecond article, whereby the nanofibers contact the first surface of thefirst article and the first surface of the at least second article at aplurality of contact points, so that forces between the nanofibers andthe first surface of the first article and the first surface of the atleast second article adhere the articles together (i.e., wherein suchforces between the articles (e.g., via the nanofibers) are greater thanforces between the articles in the absence of the nanofibers). Intypical embodiments such forces comprise van der Waals forces and/orfriction forces (e.g., as when a normal force is applied to thesurfaces). In such embodiments, the nanofibers are optionallynon-biological in material or, consist essentially of a non-biologicalmaterial. In other words, the nanofiber is not, e.g., protein,carbohydrate, lipid, or combinations thereof.

In such typical methods of joining two or more articles herein suchfirst articles can comprise a surface of one or more medical device andsuch second surfaces can comprise one or more biological tissue (e.g.,tissue (such as a vessel, an organ, bone, flesh, plant material, etc.)from an biological organism). Such biological tissue can be within anorganism (i.e., in vivo or in planta) or can be outside of an organism(i.e., ex vivo, in vitro, or ex planta). Furthermore, such biologicaltissue can comprise an entire organ (e.g., a whole liver) or cancomprise part(s) of an organ (e.g., a biopsy sample or a lobe form aliver). Also, the surface (i.e., comprising the nanofibers) canoptionally touch just a small area of the biological tissue (e.g., aswhen a probe or retractor touches an internal organ) or can touch largepercentages or even the entirety of the biological tissue (e.g., when alaminar patch comprising adherent nanofibers is placed upon an organ orvessel, etc.). Biological tissue can optionally come from any living, orpreviously living, organism (e.g., animal, plant, amphibian, reptile,bird, mammal, primates, nonhuman primates, humans, etc.). Nonlimitingexamples of such devices optionally comprise, e.g., clamps (e.g.,vasculature clamps, c-clamps, barrel clamps, circular clamps, etc.),stents, shunts, probes, retractors, patches and/or bandages, laminarsheets, medical meshes, etc. In typical embodiments, the surface(s) ofthe device which adhere to the biological tissue (s)comprise nanofibersurfaces. Thus, for example, in embodiments comprising stents, theadherent nanofiber surface s typically the surface that comes intocontact with the biological tissue, e.g., a blood vessel, a meatus, aduct, etc. For example, a stent going inside a blood vessel wouldtypically comprise adherent nanofiber surfaces on the outside portion ofthe stent that would come into contact with the inside of the vessel.

In yet other aspects herein, the invention comprises an adherent (oradhering or adhesive) device comprising a first article (having at leasta first surface), at least a second article (having at least a firstsurface) and, a layer of nanofibers disposed between the first surfaceof the first article and the first surface of the at least secondarticle, whereby the nanofibers contact the first surface of the firstarticle and the first surface of the at least second article at aplurality of contact points, such that forces between the nanofibers andthe first surface of the first article and the first surface of the atleast second article adhere the articles together (i.e., wherein suchforces between the articles are greater than forces between the articlesin the absence of the nanofibers). In some embodiments, one or more ofthe first article and the at least second articles comprise thenanofibers, while in yet other embodiments, the nanofibers are betweenthe surfaces, but are not part of the surfaces. In optional embodiments,the nanofibers are optionally non-biological in material or, consistessentially of a non-biological material. In other words, the nanofiberis not, e.g., protein, carbohydrate, lipid, or combinations thereof. Intypical embodiments the forces comprise van der Waals forces and/orfriction forces. Such devices also include wherein one or more of thefirst surface and the at least second surface comprise a plurality ofnanofibers, and also wherein physical contact between the first and atleast second substrate produces a van der Waals attraction and/orfriction force between the surfaces. In some embodiments, suchattraction can comprise from at least about 0.1 newton per centimeter²to at least about 100 newtons per centimeter², from at least about 0.5newton per centimeter² to at least about 50 newtons per centimeter²,from at least about 1 newton per centimeter² to at least about 25newtons per centimeter², or from at least about 2 newtons percentimeter² to at least about 10 newtons per centimeter². In certainaspects, embodiments can comprise hollow nanotubular structures and thenanofibers can optionally comprise one or more associated moiety(optionally a functional moiety, e.g., one which causes a van der Waalsattraction and or a friction force between the nanofiber and one or moreof the surfaces to be greater than a van der Waals attraction and/orfriction force between the nanofiber and such surface in the absence ofthe moiety). In some embodiments, the second article can comprise one ormore of: a metal, a plastic, a ceramic, a polymer, silicon, quartz,glass, wood, biological tissue, plant tissue, animal tissue, bone,stone, ice, a composite material, etc. Such devices can comprise thosefor grasping (e.g., grasping the at least second article). For example,the second article can comprise a biological tissue which can be grasped(e.g., controllably adhered) to the first article (e.g., a probe,laminar patch, etc.). Such controllable adherence can optionally betemporary (e.g., for a limited time) or can be essentially permanent, orcan last only as long as selected conditions exist (e.g., environmentalor milieu conditions around the adherence area). Such devices can alsooptionally comprise those for positioning two or, more articles (e.g.,biological tissues). For example two tissues can optionally bepositioned relative to one another, e.g., as in wound closure, etc. Suchdevices can comprise any of a number of medical devices (e.g., screws,nails, staples, probes (e.g., touch probes), laminar sheets (e.g.,bandages, patches, laminar strips, etc.)). In yet other embodiments,such devices can optionally include wherein the second article also hasat least a second surface and wherein the device also has at least athird article (with at least a first surface) and also wherein a secondlayer of nanofibers is disposed between the second surface of the secondarticle and the first surface of the third article. Thus, in suchembodiments, the nanofibers also contact the second surface of thesecond article at a plurality of contact points and the first surface ofthe at least third article at a plurality of contact points so thatforces between the nanofibers and the second surface of the secondarticle and the first surface of the third article adhere the articlestogether. In typical embodiments, the adherent forces between thearticles is greater than an adherent force between the articles in theabsence of nanofibers. Such devices can also optionally comprise medicaldevices. For example, the first and third articles (and optionallyadditional articles) together can comprise a clamp (e.g., vasculatureclamps, c-clamps, barrel clamps, etc.), a binding staple, a pair offorceps, a vise grip, a circular clamp, a barrel clamp, a medical clip,etc.

These and other objects and features of the invention will become morefully apparent when the following detailed description is read inconjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Displays a photomicrograph of an exemplary adherent nanofiberstructure of the invention.

FIG. 2, Panels A and B: Schematically illustrate the contact and van derWaals attractions and/or friction forces between nanofibersand/substrate surfaces.

FIG. 3, Panels A, B, C and D: Schematically illustrate various conceptsof intimate contact between nanofibers and substrate surfaces.

FIG. 4: Schematically illustrates construction and design of anexemplary device embodiment of the invention.

DETAILED DESCRIPTION

As stated previously, contact adhesives are often based on soft, stickypolymers that conform to surfaces and adhere through van der Waalsforces. Unfortunately, common contact adhesives are subject to a numberof limitations. For example, the layer of such contact adhesive neededto adhere materials together is usually hundreds of microns tomillimeters thick and such adhesives can soften with increasedtemperature. Such typical contact adhesives can also often leaveunwanted residues on surfaces or even outgas over time.

Typical contact adhesives rely on low modulus polymers having low glasstransition temperatures. Such contact adhesives, thus, can conform tosurfaces on a nanometer scale and form van der Waals bonds at ambientapplication temperatures. However, the low modulus of the polymers oftenleads to poor load bearing capabilities, softening of the adhesive atelevated temperatures, and brittleness at low temperatures.Additionally, typical adhesive compounds or mixtures often includetackifiers (e.g., coumarone/indene resins, phenol/terpine resins, etc.)to increase adhesion. Unfortunately, such tackifiers are often volatile,and therefore reduce the utility of such adhesives in medicalapplications, aerospace applications, clean room applications and thelike

Other common types of adhesive compounds include, e.g., two-partreactive adhesives (such as epoxies) and solvent-based or heat-activatedadhesives. These types of adhesive compounds often require at least amoderate level of skill to apply and can often release vapors until theyare cured or set. The vapors released can be hazardous and/or toxic toanimal/plant life or can cause decay of nearby materials such asplastics or fibers which come into contact with the vapors. If astructural or covalent bond is desired, these adhesive compounds alsooften require primers or coupling agents to prepare the surfaces to bebound before the liquid adhesive is applied.

Another disadvantage to common adhesive compounds is that theyexperience shrinkage during cure or polymerization. The shrinkage canbe, e.g., up to 2–5% on epoxies, etc. Shrinkage can be extremelydetrimental in many situations. For example, adhesive shrinkage cancause misalignment of surfaces and even material breakage. Additionally,many common adhesive compounds cannot be used in medical applications orsettings because of their toxic/irritative nature and/or because theywill not adhere under medical conditions.

The current invention comprises adherent materials and methods ofadhering two or more articles, materials, or surfaces together whileavoiding such problems as, e.g., thick adhesive layers, volatility, theperformance restrictions of low modulus/low glass transition temperaturematerials, etc. The adherent materials and methods of the invention are,depending upon grammatical context and the like, also sometimes referredto herein as adhesion materials and methods, or even adhesive materialsand methods. However, it will be appreciated that similarity totraditional “contact adhesives” etc. is not implied, nor should beinferred.

Without being bound to a particular theory or mechanism of operation,the concept of nanofiber adhesion of the invention is believed tooperate on the principle that even high modulus materials (e.g.,silicon), when present as fine enough nanofibers, will be compliantenough to allow close access between the fibers and a secondarysubstrate. This closeness activates van der Waals forces between thefibers and the secondary surface and so generates adhesion between thenanofibers and the secondary surface. Of course, if the nanofibers areattached (either covalently or through van der Waals forces, etc.) to afirst substrate, then the first and second substrates will be adheredtogether (e.g., via the nanofibers). In other embodiments, it isbelieved that friction forces created between the high surface areabetween the nanofibers and an opposing surface optionally joins thesurfaces together (e.g., prevents their movement relative to oneanother, prevents slipping, etc.), e.g., when normal force is applied.As explained in greater detail below, the nanofibers involved hereinallow greater contact between surfaces than would otherwise be the case.This is because the individual fibers are rigid enough to “stand up”from one surface and touch the other surface and compliant enough tobend/give, etc. to touch the various irregularities in the othersurface, thus, making greater contact than would otherwise occur. See,discussion of FIG. 3 below. This increase in intimate surface areacontact (i.e., touching) between the surfaces can therefore lead toincreased van der Waals forces and/or increased friction between thesurfaces.

Although the current invention is described generally in terms ofadhesion and joining of articles, etc., it will be appreciated that suchterms, and, thus, the present invention, encompass more transientassociations between surfaces, e.g., providing for enhanced gripping orfriction between surfaces, that may be applied to myriad differentapplications including those specifically described herein. For example,grasping/holding of objects, prevention of slipping of surfaces past oneanother (e.g., when a normal force is applied between the objects), etc.are all encompassed within the current invention.

As stated previously, some recent research in adhesion, see, e.g., K.Autumn et al., Nature (2000) 405:681–685, has focused on the physicalsurface structures of gecko feet. The gecko's foot surfaces, which insome aspects are similar to synthetic nanofibers, have been offered asan explanation for the gecko's amazing climbing ability. As shown in theExamples below, this principle (i.e., adhesion through physical surfacestructure rather than exuded polymers, or other similar contactadhesives, etc.) has been expanded and proven for nanofibers (e.g.,crystalline nanofibers, etc.). See, below. As explained, the conceptsand uses of the current invention are also optionally used with othermaterials such as carbon nanotubes and metallic nanofibers, etc. andother materials that combine the desired properties of rigidity andcompliance. Typically, in some preferred embodiments, the materialscomprising the nanofibers are non-biological materials, e.g., are notproteins, carbohydrates, lipids, etc., or combinations thereof.

The close proximity that the nanofibers achieve to the secondary surfacealso, in some embodiments, allows covalent bonding when the two surfacesare appropriately functionalized. See, below. Such covalent bondingpreviously has only been done through use of high forces and pressuresand between hard surfaces (i.e., to generate the intimate contactneeded) or with liquid systems. However, as explained herein, whennanofibers comprised of an appropriately rigid material, which alsocomprises the appropriate compliance (e.g., crystalline nanofibers) areattached to a first substrate and are contacted with a second substrate,they adhere instantly and form a structural bond. The nanofibersubstrates herein can be adhered to a wide variety of secondarysubstrates including glass, steel and plastic, or more generally,ceramics, metals, polymers, etc., as well as biological tissue, withsignificant adhesion. Of course, it will be appreciated that the greatlyincreased surface areas involved in the contact betweennanofibers/surface, etc. can also allow for a stronger bond whentraditional adhesive substances are applied (e.g., as when a traditionalpolymer adhesive is used in conjunction with the nanofiber surfacesherein).

As will be apparent from the descriptions and figures herein, preferredembodiments of the adherent nanofibers (and nanofiber devices/methods)of the invention differ structurally from naturally occurring adherentarrangements such as setae found on geckos, etc. and from adhesivesystems derived from, or based upon, such naturally occurring setae.See, e.g., U.S. Patent Publication No. US2004/0005454A1. For example,while geckos and other derived constructs are made up of spatulaeattached to shafts and/or stalks, preferred embodiments of the currentinvention rely upon nanofibers and their interaction with substrates toproduce adherence. In other words, preferred embodiments of theinvention do not comprise multiple shaft/stalk constructions (e.g.,their construction is not a spatula on a shaft/stalk or an array ofspatulae on a shaft/stalk). Additionally, in typical embodiments of thecurrent invention, the nanofibers do not comprise enlargements at theirends, as are present with spatulae of geckos and other constructs basedupon or derived therefrom. Thus, in preferred embodiments herein, thenanofibers do not comprise, e.g., bulbous swellings, flattenings, orembossments of their tips, or extended tip surfaces such as paddles,spheres, flattened segments of spheres, etc.

In typical embodiments herein, a layer of nanofibers is provided betweentwo or more surfaces that are to be joined or adhered. The layer ofnanofibers form coupling interactions with the surfaces, thus,joining/adhering them together. Providing the nanofibers between thesurfaces is optionally accomplished by providing the fibers covalentlycoupled to a first surface (e.g., by growing nanofibers directly on thefirst surface or by, e.g., separately covalently attaching the fibers tothe first surface), followed by mating the fiber-covered surface with asurface of a second article or material. Additionally and/oralternatively, nanofibers are optionally deposited on one or bothsurfaces and permitted to associate with the initial surface by the samemechanism which is ultimately exploited to couple the second surface tothe first surface (e.g., van der Waals forces, friction forces, or thelike). Other embodiments comprise wherein nanofibers are grown on and/ordeposited upon one or both sides of a flexible foil, flexible sheet, orthe like which is inserted between two or more articles and, thus, formsa bond between the nanofibers on the flexible foil and surfaces of thetwo or more articles. Other embodiments comprise nanofibers present onboth surfaces of articles to be joined. One of skill in the art willreadily grasp the various permutations of nanofiber placement/depositionupon various surfaces, interstices, etc. comprised within the invention

In some embodiments, the invention involves contacting a first surfaceand at least a second surface, so that van der Waals forces cause thesurfaces to adhere together. Of importance in such embodiments herein isthat the first surface (and in some embodiments the second surface also)comprises a plurality of nanofibers attached to, or associated with, thesurface. The presence of the nanofibers allows a much greater surfacearea of contact between the two surfaces and the intimate contact thusformed allows van der Waals forces to adhere the surfaces to one anotherand/or allows increased friction between the surfaces (or keeps thesurfaces from sliding past one another, etc.). As explained above, otherembodiments herein comprise nanofibers deposited between two surfaces,etc. See, above.

In typical embodiments herein, the surfaces (i.e., the surfaces to beadhered) and the nanofibers on the surfaces (whether on one surface oron both surfaces, free nanofibers deposited between the surfaces, or ona third surface between the first and second surfaces) can optionallycomprise any number of materials. The actual composition of the surfacesand the nanofibers is based upon a number of possible factors. Suchfactors can include, for example, the intended use of the adheredsurfaces, the conditions under which they will be used (e.g.,temperature, pH, presence of light (e.g., UV), atmosphere, etc.), theamount of force to be exerted on the bond between the surfaces (as wellas the direction of such forces, e.g., normal or parallel, etc.), thedurability of the surfaces and the bond, whether the surfaces arepresent in a biological/medical setting, cost, etc. For example, theductility and breaking strength of nanowires will vary depending on,e.g., their composition. Thus, ceramic ZnO wires can be more brittlethan silicon or glass nanowires, while carbon nanotubes may have ahigher tensile strength. If the strength of the attachment of a nanowireto a substrate is lower than the van der Waals bonding strength or thefriction force when a normal force is applied, such can help determinethe strength required to break the adhesion. Again, in typicalembodiments, the nanofibers are comprised of non-biological material(e.g., they are not made up of proteins (e.g., keratin, etc.),carbohydrates, lipids, etc., or combinations thereof).

Some possible materials used to construct the nanofibers and nanofibersurfaces herein, include, e.g., silicon, ZnO, TiO, carbon, carbonnanotubes, glass, and quartz. See, below. The nanofibers of theinvention are also optionally coated or functionalized, e.g., to enhanceor add specific properties. For example, polymers, ceramics or smallmolecules can optionally be used as coating materials for thenanofibers. The optional coatings can impart characteristics such aswater resistance, improved mechanical or electrical properties or highervan der Waals forces and/or friction forces, anti-bacterial activity,etc. In other words, in some embodiments a moiety or coating added to ananofiber can act to increase the van der Waals attraction between suchnanofiber and a substrate/surface it is to be adhered to and/or canincrease friction, e.g., when a normal force is applied, between thenanofiber and a substance/surface it is to be adhered to. Additionally,in some embodiments, a moiety or coating can serve as a covalent bindingsite (or other binding site) between the nanofiber and asubstrate/surface it is to be adhered to.

Of course, it will be appreciated that the current invention is notlimited by recitation of particular nanofiber and/or substratecomposition, and that any of a number of other materials are optionallyused in different embodiments herein. Additionally, the materials usedto comprise the nanofibers can optionally be the same as the materialused to comprise the first surface and the second surface (or thirdsurface, etc.), or they can be different from the materials used toconstruct the first surface or the second surface (or third surface,etc.).

In various embodiments herein, the nanofibers involved are optionallygrown on a first substrate and then subsequently transferred to a secondsubstrate which is used in the adhesion process. Such embodiments areparticularly useful in situations wherein the substrate desired needs tobe flexible or conforming to a particular three dimensional shape thatis not readily subjected to direct application or growth of nanofibersthereon. For example, nanofibers can be grown on such rigid surfaces as,e.g., silicon wafers or other similar substrates. The nanofibers thusgrown can then optionally be transferred to a flexible backing such as,e.g., rubber or the like. Again, it will be appreciated, however, thatthe invention is not necessarily limited to particular nanofiber orsubstrate compositions. For example, nanofibers are optionally gown onany of a variety of different surfaces, including, e.g., flexible foilssuch as aluminum or the like. Additionally, for high temperature growthprocesses, any metal, ceramic or other thermally stable material isoptionally used as a substrate on which to grow nanofibers of theinvention. Furthermore, low temperature synthesis methods such assolution phase methods can be utilized in conjunction with an even widervariety of substrates on which to grow nanofibers. For example, flexiblepolymer substrates and other similar substances are optionally used assubstrates for nanofiber growth/attachment. See below for a moredetailed discussion and references.

In yet other embodiments herein, the nanofibers involved can optionallycomprise physical conformations such as, e.g., nanotubules (e.g.,hollow-cored structures), nanowires, nanowhiskers, etc. A variety ofnanofibers are optionally used in this invention including carbonnanotubes, metallic nanotubes, metal nanofibers and ceramic nanofibers(again, all preferentially of non-biological composition, see above). Aslong as the fibers involved are concurrently rigid enough to extendabove a primary surface and compliant enough (e.g., capable of moldingor conforming or bending to meet or come into contact with an unevensurface, see, discussion of FIG. 3 below) to make intimate contact witha secondary surface and have the appropriate chemical functionality(whether arising innately or through addition of a moiety to thenanofiber) to generate strong enough van der Waals forces, frictionforces, or other physical or chemical interactions to generate adhesionforces, then such nanofibers are optionally used in the invention. Thus,those of skill in the art will be familiar with similar nanostructures(e.g., nanowires and the like) which are amenable to use in the methodsand devices of the invention.

In various embodiments herein, van der Waals attraction between a firstsurface and at least a second surface can optionally comprise greaterthan about 0.1 newton per centimeter² or more (e.g., when measured inrelation to the areas of the surfaces). Of course, such van der Waalsattractions are typically (but not necessarily solely) between thenanofibers and the second surface and optionally the nanofibers and thefirst surface.

Additionally, in other embodiments herein, van der Waals forces betweenindividual nanofibers on a first surface and a second surface canoptionally comprise, e.g., from about 1 newton per centimeter² to about100 newtons per centimeter²or more. In some embodiments van der Waalsforces between individual nanofibers on a first surface and a secondsurface optionally comprise approximately 2 newtons per centimeter².Again, it will be appreciated that recitation of specific force amountsbetween surfaces and nanofibers, etc. should not be construed asnecessarily limiting. This is especially true since the presentinvention encompasses myriad nanofiber and substrate compositions whichcan optionally affect the van der Waals and other forces between thenanofibers and/or substrates which, in turn, affect the level ofadhesion involved. Furthermore, as explained below, variousfunctionalities (either inherent to the nanofibers and/or substrates oradded to the nanofibers and/or substrates) optionally act to alter thevan der Waals or other attractive forces between the nanofibers and/orsubstrates. Thus, recitation of exemplary adherent forces (e.g., 1newton per square centimeter, etc.) should not be taken as necessarilylimiting since the invention encompasses various configurations whichpresent any of a number of different levels of adherence. Typically,however, the level of adherence (e.g., whether measured as by increasesin van der Waals forces, friction forces, etc.) is greater between theadherent nanofiber surfaces of the invention than between similarsurfaces without nanofibers.

It is to be understood that this invention is not limited to particularconfigurations, which can, of course, vary (e.g., different combinationsof nanofibers and substrates and optional moieties, etc. which areoptionally present in a range of lengths, densities, etc.). It is alsoto be understood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting. As used in this specification and the appended claims, thesingular forms “a,” “an,” and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “ananofiber” optionally includes a plurality of such nanofibers, and thelike. Unless defined otherwise, all scientific and technical terms areunderstood to have the same meaning as commonly used in the art to whichthey pertain. For the purpose of the present invention, additionalspecific terms are defined throughout.

Functionalization

Some embodiments of the invention comprise nanofiber and nanofibersurfaces in which the fibers include one or more functional moiety(e.g., a chemically reactive group) attached to them. Functionalizednanofibers will bring such reactive moiety into intimate contact with asurface where it can, e.g., chemically interact with that surface,either through van der Waals forces, friction, or by binding covalentlywith a chemical group on that surface, etc. Thus, such moieties canoptionally comprise components which will form (or help form) a covalentbond between the nanofiber and the surface to which it is contacted.However, in other embodiments, the moieties are optionally groups whichincrease the dielectric constant of the nanofiber, thus, increasing thevan der Waals attraction between the nanofiber and the surface to whichit is contacted. In other words, in some embodiments the functionalmoiety acts to increase the van der Waals attraction between thenanofiber and the surface to be greater than what such force would bewithout the moiety. Conversely, in some embodiments, such moieties canact to decrease the van der Waals attraction between the nanofiber andthe surface (e.g., in uses which require a weaker adherence than wouldotherwise result without the moiety). Also, certain moieties canoptionally increase or decrease friction forces between the nanofibersand opposing surfaces, e.g., when a normal force is applied.Furthermore, the moiety attached/associated with the nanofibers can bespecific for another moiety on a surface to be contacted (e.g.,streptavidin on either the nanofiber or the surface to becontacted/matched up with biotin on the other surface or an epoxy groupmatched up with an amine group on the other surface, etc.). Those ofskill in the art will be familiar with numerous similar pairings whichare optionally used herein (e.g., amines and boron complexes, etc.).

For example, details regarding relevant moiety and other chemistries, aswell as methods for construction/use of such, can be found, e.g., inKirk-Othmer Concise Encyclopedia of Chemical Technology (1999) FourthEdition by Grayson et al (ed.) John Wiley & Sons, Inc, New York and inKirk-Othmer Encyclopedia of Chemical Technology Fourth Edition (1998 and2000) by Grayson et al (ed.) Wiley Interscience (print edition)/JohnWiley & Sons, Inc. (e-format). Further relevant information can be foundin CRC Handbook of Chemistry and Physics (2003) 83^(rd) edition by CRCPress. Details on conductive and other coatings, which can also beincorporated onto nanofibers of the invention by plasma methods and thelike can be found in H. S. Nalwa (ed.), Handbook of Organic ConductiveMolecules and Polymers, John Wiley & Sons 1997. See also, ORGANICSPECIES THAT FACILITATE CHARGE TRANSFER TO/FROM NANOCRYSTALS U.S. Ser.No. 60/452,232 filed Mar. 4, 2003 by Whiteford et al. Details regardingorganic chemistry, relevant e.g., for coupling of additional moieties toa functionalized surface of nanofibers can be found, e.g., in Greene(1981) Protective Groups in Organic Synthesis, John Wiley and Sons, NewYork, as well as in Schmidt (1996) Organic Chemistry Mosby, St Louis,Mo., and March's Advanced Organic Chemistry Reactions, Mechanisms andStructure, Fifth Edition (2000) Smith and March, Wiley Interscience NewYork ISBN 0-471-58589-0.

Thus, again as will be appreciated, the substrates involved, thenanofibers involved (e.g., attached to, or deposited upon, thesubstrates) and the like can be varied. For example, the length,diameter, conformation and density of the fibers can be varied, as canthe composition of the fibers and their surface chemistry.

Measurement of Adhesion

Adhesion between substrates and nanofibers is optionally measured in anumber of ways. By way of example, adherent properties may be measuredby a determination of the force required to separate two coupledarticles or surfaces or the force required to move/slip twojoined/adhered surfaces past one another. Systems for performing suchmeasurements include, e.g., Universal Material Test Systems availablefrom, e.g., Instron Corp. (Canton, Mass.). Those of skill in the artwill be familiar with this and other similar means of measurement ofadhesion forces (e.g., van der Waals forces, friction forces, etc.).

Alternatively, for rough measurements, adhesion can be measured byattaching weight (which applies a separating force) to one article orsurface that is joined to another. The weight is applied and heldconstant, or applied in increasing amount, until separation occurs.Comparison is then made between that measurement and a set of controls.Thus, for example, shear strength measurement is optionally determinedby applying a force parallel to the contacted surfaces. The dimensionsof the contacted areas are optionally determined and the amount of forceor weight (applied parallel to the contacted surfaces) needed to breakapart the contacted areas is measured, thus, allowing calculation of thebond strength between the surfaces. Again, those of skill in the artwill be aware of various ways to measure adherent properties, frictionproperties, etc.

Density and Related Issues

Without being bound to a particular theory of operation or mechanism ofaction, it is believed that the amount of intimate contact between twosurfaces, e.g., the areas involved in van der Waals interactions, isdirectly related to the level of adhesion between the two surfaces.Further, as alluded to above, it is believed that nanoscale fibersurfaces provide enhanced levels of intimate contact relative to planaror flat surfaces (i.e., ones without nanofiber structures), by virtue oftheir ability to make such intimate contact between the surfaces. Suchis true despite the presence of surface variations or contamination fromdust, dirt or other particulates. It will thus be appreciated that“flat” surfaces (i.e., ones without nanofiber structures, etc.) are notreally flat. They have bumps, ridges, etc. which prevent true intimatecontact which would create, e.g., van der Waals attractions, etc. See,e.g., FIG. 3 a which illustrates a hypothetical mating of two “flat”surfaces, 300 and 310. The schematic of the surfaces shows that actualintimate contact (e.g., which would create van der Waals forces) onlyoccurs at a few locations, 320. FIGS. 2 a and 2 b show that greaterintimate contact occurs between surfaces when nanofibers are used asdescribed herein, e.g., intimate contact occurs at each point, 230 or270 where a nanofiber touches surface 210 or 250. As will beappreciated, nanofibers, 220, in FIG. 2A are depicted as straightvertical nanofibers whose contact with the surfaces occurs at theirtips. FIG. 2B, however, depicts nanofibers that curve/curl, etc., andwhich can have multiple contact points with the surfaces and/or contacta surface along the side of the nanofiber, etc. This, thus, illustratesthe wide range of nanofiber types and conformations that are encompassedwithin the current invention. In FIG. 2, the nanofibers are covalentlybound to a first surface, 200 or 260, (e.g., the nanofibers are grown onsuch first surface) but such should not be construed as limiting onother embodiments herein. For example, as detailed herein, nanofiberscan be grown on a separate surface and then transferred to the surfacesto be adhered together, can be not covalently bound to either surface,etc.

Based upon the foregoing, therefore, it is expected that the amount ofintimate contact between a first substrate and a second substrate, interms of the percentage of the overlapped surface area that is involvedin such contact (also referred to herein as the “contact density” or, insome contexts, as the “percent contact” or “percent contact area”), willhave a primary effect on the strength of adhesion between the twosubstrates. In the case of a first article that includes a nanofibersurface bound to a second planar surface, such contact density would bemeasured by the percentage of area of the second substrate surface thatis intimately contacted by the nanofibers on the first surface. FIG. 3schematically illustrates the measurement of contact density using twocontacting planar surfaces (FIG. 3A), two planar surfaces that are notperfectly planar or between which some dust or dirt has been deposited(FIG. 3B), and a nanofiber surface and a planar surface (FIG. 3C showinga top view and FIG. 3D showing a side view). As can be seen in FIG. 3A,while two planar surfaces without nanofibers, 300 and 310, may seem tobe in close intimate contact, in reality, due to surface irregularities,etc., they are only in intimate contact at a few points, 320. Such fewintimate contact points are typically not enough to generate largeenough amounts of van der Waals forces, etc., to adhere the surfacestogether. The measurement of the intimate contact in 3A, thus, could beviewed as the amount or percent of the surface area of the surface of300 which is touched by the surface of 310, i.e., just the amount orpercent which consists of contact points 320. FIG. 3D shows a similarinteraction, but with a nanofiber surface of the invention. FIG. 3Dschematically displays two surfaces, 380 and 390, which are similar tothose in FIG. 3A (i.e., 300 and 310), except that one surface, 390comprises nanofibers, 395, as described herein. As can be seen, thenanofibers allow much greater contact between the surfaces and, thus,generation of greater van der Waals forces, etc.

The amount or percent of intimate contact area, 360, in FIG. 3B consistsof just that area of contact between 330 and 340. Obstacle 350 preventsother areas of intimate contact from occurring. Of course, it will beappreciated that area 360 can also be similar to 320 in enlarged view of3A (i.e., only small points of intimate contact within 360). FIG. 3Cdisplays an enlarged top view of FIG. 2A. The areas of intimate contactbetween nanofibers 220 and surface 210 are shown as dotted circles 370(from a top view). Thus, the amount or percent of intimate contact(i.e., contact density) would comprise the amount of area within circles370 (and/or percent of surface area 210 occupied by circles 370). Ofcourse, it is to be understood that FIGS. 2A, 2B, 3C and 3D, etc. aresimplified for illustrative purposes and that typical embodiments canhave a greater number of nanofibers, the nanofibers can touch surfacesvia the sides of the nanofibers, etc. See, throughout.

Also, it will be appreciated that determination of the amount ofintimate contact between two substrates that are joined, e.g., bydeposit of nanofibers between the surfaces can be viewed from the pointof view of either surface. However, if the nanofibers are covalentlyjoined or grown from a first surface, then the point of view of percentcontact, etc. is typically viewed as exampled above. Also, for joiningof surfaces that both comprise nanofiber surfaces, the amount ofintimate contact can also be viewed from the point of view of eithersurface. Again, it will be noted that various nanofibers involved cantouch one or more surface one or more times (e.g., through curving orthe like) and can touch at different angles than just perpendicular(e.g., a nanofiber can have intimate contact with a surface throughtouching the surface along the side of the nanofiber, thus, presenting amuch greater contact area than just the tip). See, e.g., FIGS. 2B and3D.

Contact density between a nanofiber surface and another surface (alsooptionally comprising nanofibers), and, thus, adhesion, will generallybe a function of, inter alia, a number of structural characteristics ofthe nanofiber surface, including the density of wires that are grown ordeposited upon the surface(s), the thickness of each fiber, and thelength and conformation of each fiber. Regardless of the mechanism ofaction of the adherent surfaces described herein, the foregoingstructural characteristics are expected to show enhanced adhesionbetween surfaces.

In terms of density, it is clear that by including more nanofibersemanating from a surface, one automatically increases the amount ofsurface area that is extended from the basic underlying substrate, andwould thereby typically increase the intimate contact area with a secondsurface. As explained in more detail below, the embodiments hereinoptionally comprise a density of nanofibers on the first (and optionallysecond) surface of from about 1 to about 1000 or more nanofibers permicrometer² of the substrate surface. Again, here too, it will beappreciated that such density depends upon factors such as the diameterof the individual nanofibers, etc. See, below. The nanowire densityinfluences the percent contact area (or contact density), since agreater number of nanofibers will tend to increase the percent contactarea between the surfaces. As explained above, the van der Waalsattraction, friction forces, etc. between the adhered surfaces relies inlarge part upon the numerous nanofibers on at least one of the surfacesand/or between the surfaces. Such density of nanofibers on a firstsurface can typically correspond in a rough fashion to a density ofcontact points on a second surface. However, as explained throughout,nanofibers which curve, etc. and touch a surface (or even more than onesurface) multiple times and/or along the side of the nanofiber will actto increase the amount of intimate contact to be greater than just thenumber of nanofibers per unit area of the first surface. Therefore, thedensity of the nanofibers herein has a bearing on the adhesion of thesurfaces because such density is one factor in the area of contactbetween the surfaces.

The percent contact between a nanofiber (or a group of nanofibers) and asecond surface comprises, e.g., the percentage of the second surface, inunit area, touched, contacted, or covered by the one or more nanofiber.Thus, if a second surface consisted of 100 square microns and wastouched by a nanofiber whose actual touching point consisted of 10square microns, then the percent contact (i.e., amount of intimatecontact) would be 10%. In some embodiments, herein, the invention cancomprise methods and devices wherein the percent contact ranges from,e.g., about 0.01% to about 50% or greater; from about 0.1% to about 40%or greater; from about 1% to about 30% or greater; from about 2% toabout 20% or greater; from about 3% to about 10% or greater; from about4% to about 5% or greater. In some embodiments herein, the percentcontact (i.e., intimate contact) optionally comprises from approximately0.1% to approximately 5% or greater. See, FIG. 3 above.

Different embodiments of the invention comprise a range of suchdifferent densities (e.g., number of nanofibers per unit area of asubstrate to which nanofibers are attached or associated). The number ofnanofibers per unit area can optionally range from about 1 nanofiber per10 micron² up to about 200 or more nanofibers per micron²; from about 1nanofiber per micron² up to about 150 or more nanofibers per micron²;from about 10 nanofibers per micron² up to about 100 or more nanofibersper micron²; or from about 25 nanofibers per micron² up to about 75 ormore nanofibers per micron². In yet other embodiments, the density canoptionally range from about 1 to 3 nanofibers per square micron to up toapproximately 2,500 or more nanofibers per square micron.

In terms of individual fiber dimensions, it will be appreciated that byincreasing the thickness or diameter of each individual fiber, one willagain, automatically increase the area of the fiber that is able to makeintimate contact with another surface, whether such contact is with afiber that is directly orthogonal to the second surface or is parallelor tangential with that other surface. The diameter of nanofibers hereincan be controlled through, e.g., choice of compositions and growthconditions of the nanofibers, addition of moieties, coatings or thelike, etc. Preferred fiber thicknesses are optionally between from about5 nanometers up to about 1 micron or more (e.g., 5 microns); from about10 nanometers to about 750 nanometers or more; from about 25 nanometersto about 500 nanometers or more; from about 50 nanometers to about 250nanometers or more, or from about 75 nanometers to about 100 nanometersor more. In some embodiments, the nanofibers comprise a diameter ofapproximately 40 nanometers. Choice of nanofiber thickness can also beinfluenced by compliance of such nanofibers (e.g., taking into accountthat nanofiber's composition, etc.). Thus, since some compositions canproduce a less compliant nanofiber at greater diameter such changes canoptionally influence the choice of nanofiber diameter.

In the case of parallel or tangential contact between fibers from onesurface and a second surface, it will be appreciated that by providingfibers of varying lengths, one can enhance the amount of contact betweena fiber, e.g., on an edge, and the second surface, thereby increasingadhesion. Of course, it will also be understood that for some fibermaterials, increasing length may yield increasing fragility.Accordingly, preferred fiber lengths will typically be between about 2microns (e.g., 0.5 microns) up to about 1 millimeter or more; from about10 microns to about 500 micrometers or more; from about 25 microns toabout 250 microns or more; or from about 50 microns to about 100 micronsor more. Some embodiments comprise nanofibers of approximately 50microns in length. Some embodiments herein comprise nanofibers ofapproximately 40 nanometer in diameter and approximately 50 microns inlength.

Nanofibers herein can present a variety of aspect ratios. See, below.Thus, nanofiber diameter can comprise, e.g., from about 5 nanometers upto about 1 micron or more (e.g., 5 microns); from about 10 nanometers toabout 750 nanometers or more; from about 25 nanometers to about 500nanometers or more; from about 50 nanometers to about 250 nanometers ormore, or from about 75 nanometers to about 100 nanometers or more, whilethe lengths of such nanofibers can comprise, e.g., from about 2 microns(e.g., 0.5 microns) up to about 1 mm or more; from about 10 microns toabout 500 micrometers or more; from about 25 microns to about 250microns or more; or from about 50 microns to about 100 microns or more

Fibers that are, at least in part, elevated above the first surface areparticularly preferred, e.g., where at least a portion of the fibers inthe fiber surface are elevated at least 10 nanometers, or even at least100 nanometers above the first surface, in order to provide enhancedintimate contact between the fibers and an opposing surface.

Again, without being specifically bound to a particular mechanism, thebonding or adherence between the surfaces or materials in manyembodiments of the current invention is believed to be due to thebonding or adherence due to van der Waals forces between nanofibers andthe surfaces or materials. Thus, the nanofibers, because of their highmodulus and compliance create a greater surface area of intimate contactbetween the surfaces than would occur without the nanofibers. This, inturn, allows greater van der Waals forces to be generated and so adherethe surfaces together. Also, without being specifically bound to aparticular mechanism, the bonding or adherence between the surfaces ofmaterials in some embodiments of the current invention is believed to bedue to increased friction forces between nanofibers and the surfaces ormaterials. Here again, the nanofibers, because of their rigidity andcompliance, create a greater surface area of intimate contact betweenthe surfaces than would occur without the nanofibers. This, in turn,allows or creates a greater friction force to be generated between thesurfaces and so increases the force required to slide the surfaces pastone another.

As explained throughout, the nanofibers involved herein can optionallybe grown on surfaces (e.g., be covalently bound to such) andinteract/bind with a second surface through van der Waals, friction orother forces (e.g., covalently binding in situations wherein thenanofibers are functionalized with moieties, etc.). In other situationsherein; nanofibers are grown on a first substrate and transferred to,and bound to, a second substrate, e.g., covalently or through van derWaals forces, friction, etc. The second substrate is then adhered to athird substrate through van der Waals forces, friction forces, or thelike between the nanofibers on the second substrate and the surface ofthe third substrate. In yet other embodiments, nanofibers are depositedupon or between substrates and attach themselves through van der Waals,or other chemical and/or physical means to both of the surfaces, thus,adhering such surfaces together.

As seen in FIG. 1, the nanofibers optionally form a complexthree-dimensional structure. Again, it will be appreciated that in otherembodiments of the invention, the nanofibers are more uniform in height,conformation, etc. The degree of such complexity depends in part upon,e.g., the length of the nanofibers, the diameter of the nanofibers, thelength:diameter aspect ratio of the nanofibers, moieties (if any)attached to the nanofibers, and the growth conditions of the nanofibers,etc. The bending, interlacing, etc. of nanofibers, which help affect thedegree of intimate contact with a secondary surface, are optionallymanipulated through, e.g., control of the number of nanofibers per unitarea as well as through the diameter of the nanofibers, the length andthe composition of the nanofibers, etc. Thus, it will be appreciatedthat the adhesion of the nanofiber substrates herein is optionallycontrolled through manipulation of these and other parameters.

It also will be appreciated that nanofibers can, in optionalembodiments, curve or curl, etc., thus, presenting increased surfacearea for contact between the nanofibers and the substrate surfacesinvolved. The increased intimate contact, due to multiple touchings of ananofiber with a second surface, increases the van der Waalsattractions, friction forces, or other similar forces ofadhesion/interaction between the nanofiber and the second substrate. Forexample, a single curling nanofiber can optionally make intimate contactwith a second substrate a number of times. Of course, in some optionalembodiments, a nanofiber can even retouch the first surface if itcurls/curves from the second surface back to the first surface. Due topossible multiple contact points (or even larger contact points, e.g.,when a curved nanofiber presents a larger intimate contact area thanjust its tip diameter, e.g., if a side length of a nanofiber touches asubstrate surface) between a single nanofiber and a secondsubstrate/surface, the intimate contact area from curled/curvednanofibers can be greater in some instances than when the nanofiberstend not to curl or curve (i.e., and therefore typically present a“straight” aspect to the second surface). Therefore, in some, but notall, embodiments herein, the nanofibers of the invention comprise bent,curved, or even curled forms. As can be appreciated, if a singlenanofiber snakes or coils over a surface (but is still just a singlefiber per unit area bound to a first surface), the fiber can stillprovide multiple, intimate contact points, each optionally with arelatively high contact area, with a secondary surface

Nanofibers and Nanofiber Construction

The term “nanofiber” as used herein, refers to a nanostructure typicallycharacterized by at least one physical dimension less than about 1000nanometers, less than about 500 nanometers, less than about 200nanometers, less than about 150 nanometers or 100 nanometers, less thanabout 50 nanometers or 25 nanometers or even less than about 10nanometers or 5 nanometers. In many cases, the region or characteristicdimension will be along the smallest axis of the structure.

Nanofibers of this invention typically have one principle axis that islonger than the other two principle axes and, thus, have an aspect ratiogreater than one, an aspect ratio of 2 or greater, an aspect ratiogreater than about 10, an aspect ratio greater than about 20, or anaspect ratio greater than about 100, 200, or 500. In certainembodiments, nanofibers herein have a substantially uniform diameter. Insome embodiments, the diameter shows a variance less than about 20%,less than about 10%, less than about 5%, or less than about 1% over theregion of greatest variability and over a linear dimension of at least 5nanometers, at least 10 nanometers, at least 20 nanometers, or at least50 nanometers. Typically the diameter is evaluated away from the ends ofthe nanofiber (e.g. over the central 20%, 40%, 50%, or 80% of thenanofiber). In yet other embodiments, the nanofibers herein have anon-uniform diameter (i.e., they vary in diameter along their length).Also in certain embodiments, the nanofibers of this invention aresubstantially crystalline and/or substantially monocrystalline. The termnanofiber, can optionally include such structures as, e.g., nanowires,nanowhiskers, semi-conducting nanofibers and carbon nanotubes ornanotubules and the like. See, above. Additionally, in some embodimentsherein, nanocrystals or other similar nanostructures can also be used inplace of more “typical” nanofibers to produce increased adherence. Forexample, nanostructures having smaller aspect ratios (e.g., than thosedescribed above), such as nanorods, nanotetrapods, and the like are alsooptionally included within the nanofiber definition herein. Examples ofsuch other optionally included nanostructures can be found, e.g., inpublished PCT Application No. WO 03/054953 and the references discussedtherein, all of which are incorporated herein by reference in theirentirety for all purposes.

The nanofibers of this invention can be substantially homogeneous inmaterial properties, or in certain embodiments can be heterogeneous(e.g. nanofibers heterostructures) and can be fabricated fromessentially any convenient material or materials. The nanofibers cancomprise “pure” materials, substantially pure materials, doped materialsand the like and can include insulators, conductors, and semiconductors.Additionally, while some illustrative nanofibers herein are comprised ofsilicon, as explained above, they can be optionally comprised of any ofa number of different materials. Again, typically the primaryconstituents comprising the nanofibers herein are not “biological”materials, e.g., they are not biological molecules such as proteins,carbohydrates, lipids, or the like.

The nanofibers herein are typically comprised of substances which possesthe appropriate rigidity (e.g., to raise the nanofibers above thesurface of a substrate) and compliance (e.g., to allow close enoughinteraction with substrate surfaces to form adherent interactions) andproduce one or more desired interaction (e.g., van der Waals attraction,friction forces, covalent binding such as through a moiety group, etc.).The composition of nanofibers is quite well known to those of skill inthe art. As will be appreciated by such skilled persons, the nanofibersof the invention can, thus, be composed of any of a myriad of possiblesubstances (or combinations thereof). Some embodiments herein comprisenanofibers composed of one or more organic or inorganic compound ormaterial. Any recitation of specific nanofiber compositions hereinshould not be taken as necessarily limiting.

The nanofibers of the invention are optionally constructed through anyof a number of different methods; a number of which are referencedherein. Those of skill in the art will be familiar with diverse methodsof constructing nanofibers capable of use within the methods and devicesof the invention. Again, examples listed herein should not be taken asnecessarily limiting. Thus, nanofibers constructed through means notspecifically described herein, but which comprise adherent nanofibersand which fall within the parameters as set forth herein are stillnanofibers of the invention and/or are used in the devices, or with themethods of the invention.

In a general sense, the nanofibers of the current invention often (butnot exclusively, see above) comprise long thin protuberances (e.g.,fibers, nanowires, nanotubules, etc.) grown from a solid, optionallyplanar, substrate. Of course, in some embodiments herein, the fibers aredetached from the substrate on which they are grown and attached to asecond substrate. The second substrate need not be planar and, in fact,can comprise a myriad of three-dimensional conformations, as can thesubstrate on which the nanofibers were grown. In some embodimentsherein, the second substrate is flexible, which, as explained in greaterdetail below, optionally aids in binding and release of substrates fromthe nanofibers.

For example, if nanofibers of the invention were grown on, e.g., anon-flexible substrate (e.g., such as some types of silicon wafers) theycould be transferred from such non-flexible substrate to a flexiblesubstrate (e.g., such as rubber or a woven layer material). Again, aswill be apparent to those of skill in the art, the nanofibers hereincould optionally be grown on a flexible substrate to start with, butdifferent desired parameters may influence such decisions. A variety ofmethods may be employed in transferring nanofibers from a surface uponwhich they are fabricated to another surface. For example, nanofibersmay be harvested into a liquid suspension, e.g., ethanol, which is thencoated onto another surface. The same van der Waals forces, frictionforces, etc., exploited for adhesion of two articles via thesenanofibers can optionally provide coupling of the fibers to this newsurface. Subsequent mating of a surface of a second article then furtherexploits such forces in joining the two articles. Additionally,nanofibers from a first surface (e.g., ones grown on the first surfaceor which have been transferred to the first surface) can optionally be“harvested” by applying a sticky coating or material to the nanofibersand then peeling such coating/material away from the first surface. Thesticky coating/material is then optionally placed against a secondsurface to deposit the nanofibers. Examples of sticky coatings/materialswhich are optionally used for such transfer include, but are not limitedto, e.g., tape (e.g., 3M Scotch® tape), magnetic strips, curingadhesives (e.g., epoxies, rubber cement, etc.), etc. Such transfermaterials are then optionally removed through various methods dependingupon the transfer materials, etc. for example, ablation, washing,de-magnetizing and other procedures can optionally be used to removetransfer materials.

The actual nanofiber constructions of the invention are optionallycomplex. For example, FIG. 1 is a photomicrograph of a nanofiberconstruction capable of use in the current invention. As can be seen inFIG. 1, the nanofibers form a complex three-dimensional pattern. Theinterlacing and variable heights, curves, bends, etc. form a surfacewhich provides many contact points between the substrates for van derWaals, friction, or other chemical/physical forces to act to adheresubstrates together. Of course, in other embodiments herein, it shouldbe apparent that the nanofibers need not be as complex as, e.g., thoseshown in FIG. 1. Thus, in some embodiments herein, the nanofibers are“straight” and do not tend to bend, curve, or curl. However, suchstraight nanofibers are still encompassed within the current invention.

As will be appreciated, the current invention is not limited by themeans of construction of the nanofibers herein. For example, some of thenanofibers herein are composed of silicon. However, again, the use ofsilicon should not be construed as necessarily limiting. The formationof nanofibers is possible through a number of different approaches thatare well known to those of skill in the art, all of which are amenableto the current invention.

Typical embodiments herein can be used with various (e.g., existing)methods of nanostructure fabrication, as will be known by those skilledin the art, as well as methods mentioned or described herein. Forexample, the various methods of creating adherent nanofibers can beperformed using nanofibers made by the methods mentioned or describedherein or via other methods. In other words, a variety of methods formaking nanofibers and nanofiber containing structures have been or canbe described and can be adapted for use in various of the methods,systems and devices of the invention.

The nanofibers herein can be fabricated of essentially any convenientmaterial (e.g., a semiconducting material, a ferroelectric material, ametal, etc.) and can comprise essentially a single material or can beheterostructures. For example, the nanofibers can comprise asemiconducting material, for example a material comprising a firstelement selected from group 2 or from group 12 of the periodic table anda second element selected from group 16 (e.g., ZnS, ZnO, ZnSe, ZnTe,CdS, CdSe, CdTe, HgS, HgSe, HgTe, MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS,SrSe, SrTe, BaS, BaSe, BaTe, and like materials); a material comprisinga first element selected from group 13 and a second element selectedfrom group 15 (e.g., GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, andlike materials); a material comprising a group 14 element (Ge, Si, andlike materials); a material such as PbS, PbSe, PbTe, AlS, AlP, and AlSb;or an alloy or a mixture thereof.

In some embodiments herein, the nanofibers are optionally comprised ofsilicon or silicon oxide. It will be understood by one of skill in theart that the term “silicon oxide” as used herein can be understood torefer to silicon at any level of oxidation. Thus, the term silicon oxidecan refer to the chemical structure SiO_(x), wherein x is between 0 and2 inclusive. In other embodiments, the nanofibers can comprise, e.g.,silicon, glass, quartz, plastic, metal, polymers, TiO, ZnO, ZnS, ZnSe,ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, MgS, MgSe, MgTe, CaS, CaSe,CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, GaN, GaP, GaAs, GaSb, InN, InP,InAs, InSb, PbS, PbSe, PbTe, AlS, AlP, AlSb, SiO₁, SiO₂, siliconcarbide, silicon nitride, polyacrylonitrile (PAN), polyetherketone,polyimide, aromatic polymers, or aliphatic polymers.

It will be appreciated that in some embodiments, the nanofibers cancomprise the same material as one or more substrate surface, while inother embodiments, the nanofibers do not comprise the same material asthe substrates. Additionally, the substrate surfaces can optionallycomprise any one or more of the same materials or types of materials asdo the nanofibers (e.g., such as the materials illustrated herein). Ofcourse, as will be noted below, surfaces can optionally comprisesubstances quite different from the nanofibers in composition, e.g.,biological materials such as human tissue, etc. can comprise a surfaceinvolved.

Some, but by no means all, embodiments herein comprise siliconnanofibers. Common methods for making silicon nanofibers (e.g., whichcan be used with the method/devices herein) include vapor liquid solidgrowth (VLS), laser ablation (laser catalytic growth) and thermalevaporation. See, for example, Morales et al. (1998) “A Laser AblationMethod for the Synthesis of Crystalline Semiconductor Nanowires” Science279, 208–211 (1998). In one example approach, a hybrid pulsed laserablation/chemical vapor deposition (PLA-CVD) process for the synthesisof semiconductor nanofibers with longitudinally ordered heterostructuresis used. See, Wu et al. (2002) “Block-by-Block Growth ofSingle-Crystalline Si/SiGe Superlattice Nanowires,” Nano Letters Vol. 0,No. 0.

In general, several methods of making nanofibers have been described andcan be applied in the methods, systems and devices herein. In additionto Morales et al. and Wu et al. (above), see, for example, Lieber et al.(2001) “Carbide Nanomaterials” U.S. Pat. No. 6,190,634 B1; Lieber et al.(2000) “Nanometer Scale Microscopy Probes” U.S. Pat. No. 6,159,742;Lieber et al. (2000) “Method of Producing Metal Oxide Nanorods” U.S.Pat. No. 6,036,774; Lieber et al. (1999) “Metal Oxide Nanorods” U.S.Pat. No. 5,897,945; Lieber et al. (1999) “Preparation of CarbideNanorods” U.S. Pat. No. 5,997,832; Lieber et al. (1998) “Covalent CarbonNitride Material Comprising C₂N and Formation Method” U.S. Pat. No.5,840,435; Thess, et al. (1996) “Crystalline Ropes of Metallic CarbonNanotubes” Science 273, 483–486; Lieber et al. (1993) “Method of Makinga Superconducting Fullerene Composition By Reacting a Fullerene with anAlloy Containing Alkali Metal” U.S. Pat. No. 5,196,396; and Lieber etal. (1993) “Machining Oxide Thin Films with an Atomic Force Microscope:Pattern and Object Formation on the Nanometer Scale” U.S. Pat. No.5,252,835. Recently, one dimensional semiconductor heterostructurenanocrystals, have been described. See, e.g., Bjork et al. (2002)“One-dimensional Steeplechase for Electrons Realized” Nano Letters Vol.0, No. 0.

It should be noted that some references herein, while not specific to“traditional” nanofibers, are optionally still applicable to theinvention. For example, background issues of construction conditions andthe like are applicable between “traditional” nanofibers and othernanostructures (e.g., nanocrystals, nanorods, etc.) which are optionallywithin the invention.

In another approach which is optionally used to construct nanofibers ofthe invention, synthetic procedures to prepare individual nanofibers onsurfaces and in bulk are described, for example, by Kong, et al. (1998)“Synthesis of Individual Single-Walled Carbon Nanotubes on PatternedSilicon Wafers,” Nature 395, 878–881, and Kong, et al. (1998) “ChemicalVapor Deposition of Methane for Single-Walled Carbon Nanotubes” Chem.Phys. Lett. 292, 567–574.

In yet another approach, substrates and self assembling monolayer (SAM)forming materials can be used, e.g., along with microcontact printingtechniques to make nanofibers, such as those described by Schon, Meng,and Bao, “Self-assembled monolayer organic field-effect transistors,”Nature 413:713 (2001); Zhou et al. (1997) “NanoscaleMetal/Self-Assembled Monolayer/Metal Heterostructures,” Applied PhysicsLetters 71:611; and WO 96/29629 (Whitesides, et al., published Jun. 26,1996).

Synthesis of nanostructures, e.g., nanocrystals, of various compositionis described in, e.g., Peng et al. (2000) “Shape control of CdSenanocrystals” Nature 404:59–61; Puntes et al. (2001) “Colloidalnanocrystal shape and size control: The case of cobalt” Science291:2115–2117; U.S. Pat. No. 6,306,736 to Alivisatos et al. (Oct. 23,2001) entitled “Process for forming shaped group III–V semiconductornanocrystals, and product formed using process”; U.S. Pat. No. 6,225,198to Alivisatos et al. (May 1, 2001) entitled “Process for forming shapedgroup II–VI semiconductor nanocrystals, and product formed usingprocess”; U.S. Pat. No. 5,505,928 to Alivisatos et al. (Apr. 9, 1996)entitled “Preparation of III–V semiconductor nanocrystals”; U.S. Pat.No. 5,751,018 to Alivisatos et al. (May 12, 1998) entitled“Semiconductor nanocrystals covalently bound to solid inorganic surfacesusing self-assembled monolayers”; U.S. Pat. No. 6,048,616 to Gallagheret al. (Apr. 11, 2000) entitled “Encapsulated quantum sized dopedsemiconductor particles and method of manufacturing same”; and U.S. Pat.No. 5,990,479 to Weiss et al. (Nov. 23, 1999) entitled “Organoluminescent semiconductor nanocrystal probes for biological applicationsand process for making and using such probes.”

Growth of nanofibers, such as nanowires, having various aspect ratios,including nanofibers with controlled diameters which can be utilizedherein, is described in, e.g., Gudiksen et al (2000) “Diameter-selectivesynthesis of semiconductor nanowires” J. Am. Chem. Soc. 122:8801–8802;Cui et al. (2001) “Diameter-controlled synthesis of single-crystalsilicon nanowires” Appl. Phys. Lett. 78:2214–2216; Gudiksen et al.(2001) “Synthetic control of the diameter and length of single crystalsemiconductor nanowires” J. Phys. Chem. B 105:4062–4064; Morales et al.(1998) “A laser ablation method for the synthesis of crystallinesemiconductor nanowires” Science 279:208–211; Duan et al. (2000)“General synthesis of compound semiconductor nanowires” Adv. Mater.12:298–302; Cui et al. (2000) “Doping and electrical transport insilicon nanowires” J. Phys. Chem. B 104:5213–5216; Peng et al. (2000),supra; Puntes et al. (2001), supra; U.S. Pat. No. 6,225,198 toAlivisatos et al., supra; U.S. Pat. No. 6,036,774 to Lieber et al. (Mar.14, 2000) entitled “Method of producing metal oxide nanorods”; U.S. Pat.No. 5,897,945 to Lieber et al. (Apr. 27, 1999) entitled “Metal oxidenanorods”; U.S. Pat. No. 5,997,832 to Lieber et al. (Dec. 7, 1999)“Preparation of carbide nanorods”; Urbau et al. (2002) “Synthesis ofsingle-crystalline perovskite nanowires composed of barium titanate andstrontium titanate” J. Am. Chem. Soc., 124, 1186; Yun et al. (2002)“Ferroelectric Properties of Individual Barium Titanate NanowiresInvestigated by Scanned Probe Microscopy” Nano Letters 2, 447; andpublished PCT application Nos. WO 02/17362, and WO 02/080280.

Growth of branched nanofibers (e.g., nanotetrapods, tripods, bipods, andbranched tetrapods) is described in, e.g., Jun et al. (2001) “Controlledsynthesis of multi-armed CdS nanorod architectures using monosurfactantsystem” J. Am. Chem. Soc. 123:5150–5151; and Manna et al. (2000)“Synthesis of Soluble and Processable Rod-, Arrow-, Teardrop-, andTetrapod-Shaped CdSe Nanocrystals” J. Am. Chem. Soc. 122:12700–12706.Synthesis of nanoparticles is described in, e.g., U.S. Pat. No.5,690,807 to Clark Jr. et al. (Nov. 25, 1997) entitled “Method forproducing semiconductor particles”; U.S. Pat. No. 6,136,156 to El-Shall,et al. (Oct. 24, 2000) entitled “Nanoparticles of silicon oxide alloys”;U.S. Pat. No. 6,413,489 to Ying et al. (Jul. 2, 2002) entitled“Synthesis of nanometer-sized particles by reverse micelle mediatedtechniques”; and Liu et al. (2001) “Sol-Gel Synthesis of Free-StandingFerroelectric Lead Zirconate Titanate Nanoparticles” J. Am. Chem. Soc.123:4344. Synthesis of nanoparticles is also described in the abovecitations for growth of nanocrystals, nanowires, and branched nanowires.Alternatively, to produce multibranched nanofibers gold film isoptionally deposited onto a nanofiber surface (i.e., one that hasalready grown nanofibers). When placed in a furnace, fibersperpendicular to the original growth direction can result, thus,generating branches on the original nanofibers. Colloidal metalparticles can optionally be used instead of gold film to give greatercontrol of the nucleation and branch formation. The cycle of branchingoptionally could be repeated multiple times, e.g., with different filmthicknesses, different colloid sizes, or different synthesis times, togenerate additional branches having varied dimensions. Eventually, thebranches between adjacent nanofibers could optionally touch and generatean interconnected network. Sintering is optionally used to improve thebinding of the fine branches. Such multibranched nanofibers could allowan even greater increase in surface area than would occur withnon-branched nanofiber surfaces.

Synthesis of core-shell nanofibers, e.g., nanostructureheterostructures, is described in, e.g., Peng et al. (1997) “Epitaxialgrowth of highly luminescent CdSe/CdS core/shell nanocrystals withphotostability and electronic accessibility” J. Am. Chem. Soc.119:7019–7029; Dabbousi et al. (1997) “(CdSe)ZnS core-shell quantumdots: Synthesis and characterization of a size series of highlyluminescent nanocrystallites” J. Phys. Chem. B 101:9463–9475; Manna etal. (2002) “Epitaxial growth and photochemical annealing of gradedCdS/ZnS shells on colloidal CdSe nanorods” J. Am. Chem. Soc.124:7136–7145; and Cao et al. (2000) “Growth and properties ofsemiconductor core/shell nanocrystals with InAs cores”J. Am. Chem. Soc.122:9692–9702. Similar approaches can be applied to growth of othercore-shell nanostructures. See, for example, U.S. Pat. No. 6,207,229(Mar. 27, 2001) and U.S. Pat. No. 6,322,901 (Nov. 27, 2001) to Bawendiet al. entitled “Highly luminescent color-selective materials.”

Growth of homogeneous populations of nanofibers, including nanofibersheterostructures in which the different materials are distributed atdifferent locations along the long axis of the nanofibers is describedin, e.g., published PCT application Nos. WO 02/17362, and WO 02/080280;Gudiksen et al. (2002) “Growth of nanowire superlattice structures fornanoscale photonics and electronics” Nature 415:617–620; Bjork et al.(2002) “One-dimensional steeplechase for electrons realized” NanoLetters 2:86–90; Wu et al. (2002) “Block-by-block growth ofsingle-crystalline Si/SiGe superlattice nanowires” Nano Letters 2,83–86; and U.S. Ser. No. 60/370,095 (Apr. 2, 2002) to Empedoclesentitled “Nanowire heterostructures for encoding information.” Similarapproaches can be applied to growth of other heterostructures andapplied to the various methods and systems herein.

The present invention can be used with structures that may fall outsideof the size range of typical nanostructures. For example, Haraguchi etal. (U.S. Pat. No. 5,332,910) describe nanowhiskers which are optionallyused herein. Semi-conductor whiskers are also described by Haraguchi etal. (1994) “Polarization Dependence of Light Emitted from GaAs p-njunctions in quantum wire crystals” J. Appl. Phys. 75(8): 4220–4225;Hiruma et al. (1993) “GaAs Free Standing Quantum Sized Wires,” J. Appl.Phys. 74(5):3162–3171; Haraguchi et al. (1996) “Self OrganizedFabrication of Planar GaAs Nanowhisker Arrays”, and Yazawa (1993)“Semiconductor Nanowhiskers” Adv. Mater. 5(78):577–579. Suchnanowhiskers are optionally nanofibers of the invention. While the abovereferences (and other references herein) are optionally useful forconstruction and determination of parameters of nanofibers for theinvention, those of skill in the art will be familiar with other methodsof nanofiber construction/design, etc. which can also be amenable to themethods and devices herein.

Exemplary Uses of Adhesive Nanofibers

The constructs and methods of the current invention are widelyapplicable to a broad range of uses, and therefore, specific mention ofuses herein should not be taken as necessarily limiting. In general, theinvention is useful to adhere two or more surfaces together and/orprevent or inhibit two or more surfaces from sliding past one another(e.g., typically when a normal force is applied). The invention isespecially useful (but is not limited to) situations/conditions that arenot conducive to use of more conventional adhesives. For example, manycommon adhesives are not useful under conditions such as hightemperature, low temperature, high or low humidity, vacuum, in medicalsettings, or other similar conditions which can adversely effect thepolymer, resin, etc. used as the adhesive. Furthermore, in certainmedical uses such as attachment of medical devices in vivo or attachmentof medical devices such as metal plates, etc. to bone or teeth, theadhesive used must be non-immunogenic, etc. For further examples of usesof nanofiber surfaces, e.g., in medical applications, etc., see, e.g.,U.S. Ser. No. 60/468,390 filed May 6, 2003, U.S. Ser. No. 60/468,606filed May 5, 2003, and U.S. Ser. No. 10/792,402 filed Mar. 2, 2004, allthree entitled “Nanofiber Surfaces for Use in Enhanced Surface AreaApplications”; U.S. Ser. No. 60/549,711 filed Mar. 2, 2004 entitled“Medical Device Applications of Nanostructured Surfaces”; U.S. Ser. No.60/541,463, filed Feb. 2, 2004 entitled “Porous Substrates, Articles,Systems and Compositions Comprising Nanofibers and Methods of Their Useand Production”; and U.S. Ser. No. 60/466,229, filed Apr. 28, 2003,entitled “Super-hydrophobic Surfaces, Methods of Their Construction andUses Therefor,” all of which are incorporated herein in their entiretyfor all purposes.

The adherent nanofibers/structures of the invention and the methods oftheir use can easily be tailored to avoid the problems concerningambient conditions and medical concerns (see, above) throughmanipulation of the parameters herein, e.g., choice of nanofibercomposition material and the like. Additionally, the nature of theinvention inherently avoids many of the previously mentioned typicalproblems (and others as well) since the adherent properties of theinvention do not rely on extraneous polymers and the like which canbreak down or creep under extreme conditions. Instead, the currentinvention optionally relies upon the van der Waals attraction and/orfriction between the nanofiber structures and surfaces. Thereforetemperature fluctuations and the like do not alter the basic adherentbonds of the invention.

In some embodiments, the invention can be used to construct climbing orhanging equipment. For example, similar to geckos, the adherentnanostructures herein can optionally be attached to equipment (e.g.,gloves, handheld pads and the like), to allow easy grip of surfaces suchas walls, ceilings, rock faces, etc. The ability of the invention to beincorporated into flexible forms allows the rocking or peeling away ofthe nanofibers from the surface to which they are adhered. Therocking/peeling changes the contact angle of individual nanofibers inrelation to the surface they are adhered to and, thus, can cause releaseof the individual fiber. Such release is, of course, quite useful intypical applications, e.g., in climbing, etc. Conversely, when releaseis not desired, the contact angle of the nanofibers is optionally notchanged and so no release occurs. Such release can also optionally occurwith devices/methods of the invention which comprise nanofiber surfacesthat are not flexible as well. In such cases, release can be achieved bychanging the contact angle, etc. of nanofibers. For example, in aclamping device or the like which incorporates nanofiber adhesionaspects of the invention, release can optionally be done by applyinggreater separating pressure at one contact area which creates aseparating force in that area which is greater than the forces adheringthe nanofibers/surfaces in that area.

This could be done by, e.g., a fulcrum/scissoring motion as is commonlyused in scissors/hemostats, etc. which have an X or V shaped body or thelike. Thus, the remaining adhering nanofibers would then be undergreater separating forces because they would be carrying a greater load(i.e., because other nanofibers were no longer in contact with theopposing surface, etc.) and could therefore be separated in a similarmanner. Another point optionally involved in release is that the changein contact angle of the nanofibers between the surfaces can go from,e.g., nanofibers which present their sides to a surface (thus, creatinggreater intimate contact and greater adherent force) to, e.g.,nanofibers which present less of their sides or just their tips to asurface (thus, creating a lower amount of intimate contact and a loweramount of adherent force). Also, in some situations involving frictionaladherence, a change in applied pressure (e.g., from lateral toperpendicular to a surface) or a removal or reduction of normal force,can optionally cause release of adhered surfaces.

Yet other possible embodiments of the current invention include“setting” or “fixing” of devices/materials into place. For example, ascrew put into a material (e.g., a metal plate) could be made much morestable and less prone to release by incorporating nanofiber adherents ofthe invention. Such incorporation could optionally be done by havingnanofibers on one or more of the screw or the screw-hole which receivesthe screw. Also, nanofibers could optionally be placed between the screwand the screw-hole, e.g., via a slurry of nanofibers or the like. See,above. Addition of nanofibers to one or more surface, or addition ofslurries or dry mixes of nanofibers, etc. could, thus, be similarly usedto adhere any number of materials (e.g., screw, nails, fasteners,interlocking devices/plates, etc.).

In yet other embodiments, the methods and devices of the invention canbe utilized in, e.g., aerospace applications, medical applications, orindustrial processing applications where creation of bonds which arestrong at an appropriate temperature, which produce little or nooutgassing and which have the potential for reuse is desired.

In yet other types of embodiments, the devices and methods of theinvention can optionally be used in applications wherein a normal forceis applied to the substrate surfaces involved, in order to produceadherence of the substrates. Thus again, in some contexts herein,“adherence,” “adhesion,” or the like can refer to prevention orinhibition of lateral or shear movement (e.g., slipping, sliding, or thelike between surfaces such as would occur between a medical clamp and atissue, between two tissues, etc.). Such embodiments can optionallydiffer from previously described embodiments in that they can requireapplication of a normal force in order to, or to help to, adhere thesurfaces. However, because of the nanofiber surfaces herein, frictionforces, etc. are believed to produce adherence at lower levels of normalforce than would be required in the absence of the nanofibers. Seeexamples below. Thus, such applications are especially useful insituations requiring adherence (again, here meaningprevention/inhibition of lateral movement, e.g., slipping, of surfaces),but which also require a delicate or gentle normal force. In otherwords, devices/methods of the invention can be used to prevent/inhibitslippage, but with application of much less normal force than wouldotherwise be required with non-nanofiber systems.

Therefore, devices and methods of the invention are optionally used inconstruction of clamps, such as those used in medical devices, hemostatsor the like. Currently jaw inserts of medical clamps are typically madeof rubber or metal. Rubber is usually the less intrusive option becauseit provides compliance (e.g., yielding or conforming to shapes due to,e.g., force applied). The addition of serrated areas or protrusions areoften used to increase localized forces on the tissue being clamped.Such features are especially used for irregular surfaces such asarteries or tissue. However, the pressure applied (i.e., normal force)to effectively close off an artery or hold tissue, etc., while keepingthe tissue, etc. within the clamp, can possibly damage thetissue/artery/etc. involved. Thus, it is desirable to minimize thepressure applied, but still produce the specific result, e.g., holding atissue, clamping an artery, etc. Optimization (e.g., reduction) of suchpressures, etc. can optionally be achieved by incorporation of nanofiberinserts in medical clamps and the like.

As one nonlimiting example, thin metal sheets (e.g., approximately 10 to150 μm and preferably 25–100 μm) which are quite flexible and resistantto permanent deformation can be used for construction of nanofiberadhesive surfaces for the clamps. Additionally such thin metal sheetsare ideal growth surfaces for nanofibers due to their high temperatureresistance. For example, stainless steel, titanium, nickel, berylliumcopper and nickel would all be candidate materials for construction ofvarious medical devices incorporating aspects of the invention. Suchthin films can be etched or stamped into precise and intricate shapes.See, FIG. 4 which gives schematics for one possible type of medicalclamp. It will be appreciated that numerous other clamp designs andformations (incorporating the concepts of the current invention) arealso possible and that the illustration in FIG. 4 should not be taken aslimiting. Secondary operations are typically done to bend and form partsof clamps into three-dimensional shapes. For a clamp insert withnanofiber adherent areas, flat parts can optionally be etched or stampedand a secondary operation can optionally be performed by bending thestrip into a C shape to make it into a channel to slide into the clampas well as using the C shape to create spring forces. Such secondaryoperations can also optionally stamp or create serrations or protrusionson the clamp. Areas that require nanofibers can then optionally be goldplated for growth of nanofibers. Thus, for example in FIG. 4, a sheet ofthin metal, 400, can be stamped or etched to produce various subparts,410, that can be formed into devices such as clamps. Once removed fromthe metal sheet, the stamped or etched parts, 410 can be manipulated invarious manners, e.g., bent to the proper conformation, 430 (which showsan end view), and nanofibers can be grown or deposited upon the correctface/aspect of the part (e.g., nanofibers can be grown aftergold-plating, etc.). The properly manipulated part (comprisingnanofibers) can then be assembled with other device parts, e.g., a clampinsert, etc., 440, to produce the device. As will be appreciated,however, numerous methods exist for creation of nanofibers for useherein (see, above) not all of which require gold plating, etc. Stampingand bending operations as would be used to create such devices areusually quite inexpensive and can result in precise high quality parts.The spring qualities and high temperature resistance of thin metals canoptionally enhance the functionality of the friction/van der Waalscharacteristics of the nanofiber devices. Again, however, it will beappreciated that the nanofiber adhesive surfaces of the invention withtheir frictional/van der Waals forces will require less clamping force(i.e., normal force) on tissues, etc, and will subsequently induce lesstissue damage. The forces (e.g., friction, etc.) can prevent sliding orslipping of medical devices, such as clamps, off of tissues, arteries,etc. which are typically coated with blood/bodily fluids that can causeslipping of ordinary clamps, etc.

As will be appreciated by those skilled in the art, the adherentsurfaces and methods herein present a wide, and deep, range ofapplications in many fields. For example, in medical settings theadherent surfaces/methods herein can be part of myriad devices for usein, e.g., surgery, as implantable devices, etc. The example sectionbelow gives but a few of the many possibilities, all of which arecontained within the current invention. In a general non-limiting sense,nanofiber adherent medical devices can be categorized as comprising,e.g., two-surface devices (one or more of which surfaces comprisenanofibers or between which nanofibers are present) in which thesurfaces adhere to one another; two-surface devices (one or more ofwhich surfaces comprise nanofibers or between which nanofibers arepresent) in which the surfaces sandwich another article, such as atissue or vessel, etc., between them; and one-surface devices whichsurfaces comprise nanofibers, or which surfaces have nanofibers betweenthem and the article (e.g., a tissue) they touch. Yet other exemplaryillustrations of, e.g., medical devices which can optionally incorporatethe adherent nanofiber devices/methods, etc. herein can be found in,e.g., U.S. Ser. No. 60/468,390, filed May 6, 2003 and U.S. Ser. No.60/468,606, filed May 5, 2003, both entitled “Nanofiber Surfaces for Usein Enhanced Surface Area Applications,” U.S. Ser. No. 60/549,711, filedMar. 2, 2004 entitled “Medical Device Applications of NanostructuredSurfaces,” U.S. Ser. No. 60/541,463, filed Feb. 2, 2004 entitled “PorousSubstrates, Articles, Systems and Compositions Comprising Nanofibers andMethods of Their Use and Production,” and U.S. Ser. No. 60/466,229,filed Apr. 28, 2003, entitled “Super-hydrophobic Surfaces, Methods ofTheir Construction and Uses Therefor,” all of which are incorporatedherein in their entirety for all purposes. Again, however, specificrecitation of specific medical devices, etc. should not be taken aslimiting, thus, myriad non-recited medical devices, etc. are also withinthe purview of, and are part of, the current invention.

Examples of nanofiber surface devices in which the surfaces touch oneanother could include, but are not limited to, e.g., those in whichtissues are separately attached to each surface (through any means) andin which the two surfaces of the device are attached to each other.Additionally, locking clamps and the like (e.g., in which the positionof the device is stabilized such as in an open, partially open or closedposition) can comprise locking mechanisms comprised of touchingnanofiber surface(s). Of course, such embodiments can optionallycomprise more than two surfaces as well.

Examples of nanofiber surface devices which clamp/grasp/hold articlescan include, e.g., typical clamp devices (e.g., hemostats, ring-clamps,etc.) which hold/grasp/immobilize tissues, etc. during medicalprocedures. In such embodiments, the surfaces of the device typicallycomprise nanofiber surfaces (and/or nanofibers are optionally placedbetween the device surfaces and the article to be held). In suchsituations, two (or more) adherent areas are created, e.g., one on eachside of the object held, between the surfaces of the device and thesides of the object. Again, such embodiments can optionally comprisemore than two surfaces.

Examples of nanofiber single surface devices can include such adherentdevices as patches, laminar bandages, shunts, stents, retractors,touch-probes, etc. In such devices, the device surface typicallycomprises the nanofiber surface and/or nanofibers are deposited betweenthe surface of the device and the object to be held/grasped, etc., e.g.,a tissue or vessel. As will be appreciated, the increased adherentand/or friction forces of the nanofiber-surfaced devices of the currentinvention provide for better stability of such devices within organisms,e.g., better stability of the devices within body cavities, meatuses,vasculature, etc. Such devices are held in place better through theaddition of nanofibers. Such patches or bandages can optionally be usedto close wounds, hold internal tissues together, etc. Additionallyretractors and touch probes (e.g., wand devices used to gently adhere tosurfaces, thus, allowing manipulation of a tissue, etc. withoutclamping) are also optional devices herein. Yet other devices withinthis category can optionally include those such as shunts, stents andthe like, e.g., used to stabilize lines, etc. within vessels or organsand/or to stabilize catheters, etc. Thus, for example, in embodimentscomprising stents, the adherent nanofiber surface is typically thesurface that comes into contact with the biological tissue, e.g., ablood vessel, a meatus, a duct, etc. For example, a stent going inside ablood vessel would typically comprise adherent nanofiber surfaces on theoutside portion of the stent that would come into contact with theinside of the vessel.

Again, those of skill in the art will be cognizant of the myriadpermutations, specializations, and embodiments of devices of the currentinvention (e.g., various types of clamps, stents, etc.)

Additionally, it will also be appreciated that such clamps and the likeare optionally used in other areas besides medical settings (e.g.,clamping of wires or of tubes in mechanical or industrial applications,etc), but which also would benefit from stable more gentle clamping thanoccurs with traditional means. Those of skill in the art will be awareof numerous other possible uses for such devices. Those of skill in theart will also be aware of many applications where the nanofiber adherentdevices can hold slippery and/or hard to grasp objects (e.g., arteries,tissue, wet tubes, etc.) with a gentle grasp as opposed to a harshclamping (e.g., harsh because of high pressure and/or sharp ridges orpoints or the like), which is required with other current devices, toovercome slipperiness issues and provide a firm hold.

Kits/Systems

In some embodiments, the invention provides kits for practice of themethods described herein and which optionally comprise the substrates ofthe invention. In various embodiments, such kits comprise a container orcontainers with, e.g., one or more adhesion substrate as describedherein, one or more device comprising an adhesion nanofiber substrate,etc. (e.g., a medical device such as a sterile clamp, etc.).

The kit can also comprise any necessary reagents, devices, apparatus,and materials additionally used to fabricate and/or use an adhesionnanofiber substrate, device or the like.

In addition, the kits can optionally include instructional materialscontaining directions (i.e., protocols) for the synthesis of adhesionnanofibers and/or adding of moieties to adhesion nanofibers and/or useof adhesion nanofiber structures and/or devices. Such instructions canoptionally include, e.g., instructions on proper handling and use,sterilization, etc. of a medical device or the like. Preferredinstructional materials give protocols for utilizing the kit contents(e.g., to use the adhesion nanofibers or adhesion nanofiber methods ofthe invention). Instructional materials can include written material(e.g., in the form of printed material, material stored on CD, computerdiskette, DVD, or the like) as well as access to an internet site whichcontains the appropriate instructions.

In certain embodiments, the instructional materials teach the use of thenanofiber substrates of the invention in the construction of one or moredevices (such as, e.g., sealing devices, attachment devices, medicaldevices, etc.).

EXAMPLES Example 1 Construction of an Adherent Nanofiber Substrate

Silicon nanofibers of approximately 40 nanometer in diameter and 50 umin length were grown on a four inch silicon wafer through a standard CVDprocess using gold colloids (see, e.g., above). The fiber density wasapproximately 2 nanofibers per square micron. To test the adhesionability of the silicon nanofiber wafer, a microscope slide was suspendedin a vertical orientation above a lab bench. A 2 centimeter×1 centimeterpiece from the above silicon wafer containing the nanofibers was lightlypressed against the glass slide (with the nanofiber surface touching theglass slide). Thus, the top centimeter of the nanofiber wafer wasexposed to the glass while the other centimeter was not in contact withthe glass. A 200 gram weight was then attached to the free end of thesilicon wafer via a binder clip. The weight was allowed to hang freely,thus, exerting a stress of 2 newtons on the nanofiber/glass interface.There was no measurable movement in the nanofiber joint in 10 days.

Example 2 Construction of an Adherent Nanofiber Substrate

Silicon nanofibers of approximately 40 nanometers in diameter and 50 umin length were grown on a 4 inch silicon wafer by the standard CVDprocess using gold colloids. See, e.g., above. The fiber density wasapproximately 2 nanofibers per square micron. To test the adhesionability of the silicon nanofiber wafer to itself, two 2×1 centimeterpieces were cut from the silicon wafer containing the nanofibers. Onecentimeter of the fiber surface of each piece was lightly pressedtogether. One free end of the pressed pieces was clamped in a vice on aring stand and a 100 gram weight was hung from the opposite end. Theweight was allowed to hang freely, thus, exerting a stress of 1 newtonon the nanofiber surface/nanofiber surface interface. There was nomeasurable movement in the nanofiber joints in 10 days.

Example 3 Reuse of Adherent Nanofiber Substrates

The nanofiber substrate in Example 1 was pulled away from the glass in aperpendicular direction. It was then pressed against a second suspendedpiece of glass and through a similar process was shown to again hold 2newtons of force.

Example 4 Reuse of Adherent Nanofiber Substrates

A nanofiber substrate prepared as explained in Example 1 was pressedagainst a variety of substrates including stainless steel, Formica®,painted metal and Teflon®. The substrate exhibited enough adherent forceto support its own weight for all of the materials except Teflon® ofwhich it slipped off.

Example 5 Coefficient of Friction of Adherent Nanofiber Substrates

A Micro Scratch Tester (Micro Photonics, Torrance, Calif.) was used todetermine the difference in coefficient of friction between a nanofibersurface of the invention and a similar surface without nanofibers. Aglass surface (i.e., a borosilicate glass microscope slide) that waschemically similar to silicon dioxide nanowires (i.e., one possibletype/construction of nanofibers of the invention) was tested against ananofiber surface similar to those used in previous example, supra. Thenanofiber surface had a coefficient of friction of 2.0 while the glassslide (without nanofibers) had a coefficient of friction of 0.08.

Example 6 Friction Forces/Gripping of Adherent Nanofiber Substrates

A 5-inch piece of fresh pig aorta obtained commercially was clamped ateach end while immersed in a tank of whole milk. A pair of typicalmedical clamps (Novare® Medical, Cupertino, Calif.) was clamped on tothe center of the aorta. These clamps, as is typical with many medicalclamps, use silicon rubber disposable inserts in the “jaws” of theclamp. Such devices are currently considered to be state of the art fortraction/holding of tissues in medical settings. The “clamp force” ofthe Novare® clamp (i.e., the pressure exerted upon the vessel) wasdetermined by the jaw position of the clamps. In other words, the jawposition (how tightly the jaws were clamped together) determined theclamping force upon the aorta. The handle of the clamps was attached toa load cell that was programmed to pull the clamps at a set rate normalto the aorta. The maximum force reached before the clamps slipped off ofthe aorta was thus measured.

The test was repeated with the Novare® clamps three times. The averageforce applied to cause slippage of the clamps off of the aorta was 4lbs. The clamp inserts were then changed from the traditional siliconrubber to a nanofiber surface of the invention. The adherent nanofibersurface comprised silicon nanowires grown on a silicon wafer. Thenanofibers in such example were of 40 nm average diameter and 30 micronsaverage length and were present at about 5 nanofibers per square micronof substrate surface. The clamp surface area of the nanofiber surfacewas the same as the surface measured for the rubber inserts.Additionally, the jaw position of the clamps was equivalent in eachtesting. The average force required to slip the nanowire surface off ofthe aorta was 7 lbs. No major differences were observed in regard totissue damage on the aorta from the clamping action. Additionally, bothhydrophilic and hydrophobic nanofiber surfaces produced similar adherentaction upon the vessel.

As another control, the silicon nanowire surfaces were reversed in theclamps so that the back of the wafer (i.e., without nanofibers) wasexposed to the aorta. In such example, a force of only 2 lbs wasrequired to slip the clamp off of the vessel.

While the foregoing invention has been described in some detail forpurposes of clarity and understanding, it will be clear to one skilledin the art from a reading of this disclosure that various changes inform and detail can be made without departing from the true scope of theinvention. For example, all the techniques and apparatus described abovecan be used in various combinations. All publications, patents, patentapplications, or other documents cited in this application areincorporated by reference in their entirety for all purposes to the sameextent as if each individual publication, patent, patent application, orother document were individually indicated to be incorporated byreference for all purposes.

1. A method of adhering a surface of a medical device to a biologicaltissue surface, the method comprising: i) providing a medical devicehaving at least a first surface and a plurality of silicon nanofibersassociated with the first surface; and ii) contacting the medical deviceto a biological tissue surface whereby the nanofibers contact thebiological tissue surface at a plurality of contact points, such thatforces between the nanofibers and the biological tissue surface adherethe medical device to the biological tissue surface.
 2. The method ofclaim 1, wherein the biological tissue comprises one or more of: avessel, an organ, bone, flesh, or plant material.
 3. The method of claim1, wherein the biological tissue comprises an animal tissue, anamphibian tissue, a reptilian tissue, an avian tissue, a mammal tissue,a non-human primate tissue, or a human tissue.
 4. The method of claim 1,wherein the medical device comprises a clamp, a stent, a shunt, a probe,a retractor, a patch, a bandage, or a medical mesh.
 5. An adherentmedical device, the device comprising: at least a first surfacecomprising a plurality of silicon nanofibers, whereby the nanofibers arearranged on the first surface to contact a biological tissue surface ata plurality of contact points at least a portion of which are located ona side surface of the nanofibers, such that forces between thenanofibers and biological tissue surface adhere the medical device tothe biological tissue surface substantially by van der Waals forcesbetween the nanofibers and the biological tissue surface.
 6. The deviceof claim 5, wherein the van der Waals forces comprises from at leastabout 0.1 newton per centimeter² to at least about 100 newtons percentimeter².
 7. The device of claim 5, wherein the van der Waals forcescomprises from at least about 0.5 newton per centimeter² to at leastabout 50 newtons per centimeter².
 8. The device of claim 5, wherein thevan der Waals forces comprises from at least about 1 newton percentimeter² to at least about 25 newtons per centimeter².
 9. The deviceof claim 5, wherein the van der Waals forces comprises from at leastabout 2 newtons per centimeter² to at least about 10 newtons percentimeter².
 10. The device of claim 5, wherein the nanofibers comprisehollow nanotubular structures.
 11. The device of claim 5, whereinsubstantially all nanofibers comprise one or more associated moiety. 12.The device of claim 5, wherein the one or more moiety comprises afunctional moiety.
 13. The device of claim 12, wherein the functionalmoiety creates a van der Waals attraction between the nanofiber and thebiological tissue surface, greater than a van der Waals attractionbetween the nanofiber and such surface in the absence of the moiety. 14.The device of claim 12, wherein the functional moiety creates a frictionforce between the nanofiber and the biological tissue surface greaterthan a friction force between the nanofiber and such surface in theabsence of the moiety.
 15. The device of claim 5, wherein the biologicaltissue comprises one or more of: plant tissue, animal tissue, or bonetissue.
 16. The device of claim 5, wherein the medical device comprisesa device for grasping the biological tissue.
 17. The device of claim 16,wherein grasping comprises controllably adhering such tissue to themedical device.
 18. The device of claim 16, wherein grasping comprises acontrollable period of time.
 19. The device of claim 5, wherein thedevice comprises a device for controllably positioning two or morebiological tissues.
 20. The device of claim 19, wherein the devicepositions the two or more tissues relative to one another.
 21. Thedevice of claim 5, wherein the medical device comprises a screw.
 22. Thedevice of claim 5, wherein the medical device comprises a nail.
 23. Thedevice of claim 5, wherein the medical device comprises a staple. 24.The device of claim 5, wherein the medical device comprises a probe. 25.The device of claim 5, wherein the medical device comprises a laminarsheet.
 26. The medical device of claim 5, wherein the medical devicecomprises a clamp, a binding staple, a forceps, a vise grip, a circularclamp, a barrel clamp, or a clip.
 27. The device of claim 5, wherein thenanofibers are grown on the first surface of the medical device.
 28. Thedevice of claim 27, wherein the nanofibers are grown by a VLS growthprocess.
 29. The device of claim 5, wherein the nanofibers have a lengthof at least about 50 microns.
 30. The device of claim 5, wherein thenanofibers are coated with one or more functional moiety.
 31. The deviceof claim 30, wherein the one or more functional moiety is adapted toenhance the mechanical strength of the nanofibers.